1. Field of the Invention
The present invention relates generally to blast cleaning machines, and particularly to, but not by way of limitation, to hand-held blast cleaning machines.
2. Description of Related Art
Various machines for blast cleaning surfaces are known in the art. For example, U.S. Pat. No. 3,034,262 issued to Pawlson discloses a resurfacing and finishing machine. The Pawlson machine has no mechanism for automatically blocking the flow of abrasive material when the machine is intentionally or accidentally released. Moreover, the Pawlson machine has no air wash for removing dust and debris from the abrasive material.
Another example is U.S. Pat. No. 3,900,969, issued to Diehn and disclosing a portable apparatus for blast cleaning. The Diehn apparatus is not designed to be hand-held. In fact, it is so unwieldy that it is supported on casters. In addition, the Diehn apparatus may only be used on surfaces which are somewhat vertically disposed in order for the hopper to gravity feed abrasive material to the blast wheel.
A third example of related art is U. S. Pat. No. 4,020,596, which is issued to Bergh and discloses a convertible blast cleaning unit. The Bergh unit has modules for converting the unit between side-blasting mode and up-blasting mode.
The Bergh unit is designed for cleaning large areas, such as the hulls of ships. Accordingly, the Bergh machine is not suitable for use as a hand-held device. Because only up-blasting and side-blasting are required for cleaning the hull of a ship, the Bergh unit is not designed for conversion to blast downward.